Hydraulic pump or motor device plungers

ABSTRACT

A plunger for a pump or a motor comprising a plunger body having a hollow interior having a generally cylindrical inner surface and a filler body molded in the interior and prevented from axial, spiral and circumferential displacement relative to the plunger body by two portions of the inner surface differently shaped from each other and also from the generally cylindrical portions. The two portions may be two spiral grooves having different pitches from each other, or a groove having circumferentially varying depth. These grooves are radially deeper than the inner surface at the open end of the hollow interior.

United States Patent Dec. 28, 1968, Japan, No. 43/114438 HYDRAULIC PUMPOR MOTOR DEVICE PLUNGERS 8 Claims, 4 Drawing Figs.

US. Cl 92/172,

92/248 Int. Cl F16j l/00 Field of Search 92/248,

Primary Examiner-Martin P. Schwadron Assistant Examinerlrwin C. CohenAttorney-Steinberg and Blake ABSTRACT: A plunger for a pump or a motorcomprising a plunger body having a hollow interior having a generallycylindrical inner surface and a filler body molded in the interior andprevented from axial, spiral and circumferential displacement relativeto the plunger body by two portions of the inner surface differentlyshaped from each other and also from the generally cylindrical portions.The two portions may be two spiral grooves having different pitches fromeach other, or a groove having circumferentially varying depth. Thesegrooves are radially deeper than the inner surface at the open end ofthe hollow interior.

HYDRAULIC PUMP R MOTOR DEVICE PLUNGERS This invention relates in generalto fluid pressure translating device of the reciprocating type, and moreparticularly to a new and improved plunger construction particularlyadapted for use in hydraulic pumps or motors.

Generally speaking, the plunger-type hydraulic pump is characterized bya higher pressure generated thereby than pressures generated by the gearpump or the vane pump. In such a plunger-type hydraulic pump where theoperating liquid medium is highly pressured, it is desirable that thevolume of the pressured liquid medium is as small as possible on theground that it is impossible to neglect an influence of compressibilityof the liquid medium on the volumetric efficiency of the pump. In a pumpof the class described having a small suction stroke volume, if a largeoutput per unit time is required, it is necessary to rotate the pump ata correspondingly high speed. As the plunger of the pump reciprocatesonce per one rotation of the driving shaft of the pump, the higher therotating speed the larger the inertia force, so that it is necessary tocorrespondingly strengthen the plunger reciprocating mechanism. However,it is undesirable to weight the plunger, and therefore, it is requiredto reduce the inertia force of the plunger. It is well known that aninertia force of a body proportionates to a mass thereof and the squareof the velocity thereof. Under these circumstances, many attempts havebeen proposed to reduce the mass of the plunger in such a manner thatthe major internal portion of the plunger is removed for lightening theplunger as light as possible. However, if the plunger is provided with ahollow interior opened to the liquid medium, the volumetric efficiencybecomes inferior due to the compressibility of the liquid medium filledin the hollow interior as set forth hereinbefore. In view of this, it isundesirable to provide a hollow interior in the plunger but it isdesirable to form a solid plunger. In order to solve the contradictoryrequirements, such a plunger as having a hollow interior filled with afiller body of a light weight and a high bulk modulus has been proposedin order to make a pump possible to rotate at a high speed under a highpressure, for example, as disclosed in our U.S. Pat. application, Ser.No. 754,184, and now abandoned.

However, a plunger having a hollow interior simply filled with a fillerbody is disadvantageous because it is probable that the filler body isremoved from the hollow interior due to vibration caused by the highspeed operation and incomplete connection of the filler body with theplunger body. If the filler body is removed from the hollow interior, itis natural that the filler body will displace relative to the hollowinterior as far as the latter is simply cylindrical. In accordance withthe invention of the U.S. Pat. application, Ser. No. 754,184, the axialdisplacement of the filler body relative to the hollow interior isprevented by means of a snap ring. However, the circumferentialdisplacement or rotation of the filler body relative to the hollowinterior also probably occurs and is to be prevented. When the fillerbody rotates in the hollow interior relative thereto, it is apparentthat these members are worn, and therefore, various disadvantagestroubles such as shakiness, jolt, noise, etc., are caused before long.

The primary object of this invention is to provide a plunger having asmall inertial mass without lowering the volumetric efficiency and thedurability in operation at a high speed for use in the plunger pump ormotor, overcoming the abovestated drawbacks.

Briefly stated in accordance with one aspect of this invention, there isprovided a plunger for a pump or motor compris ing a plunger body havinga hollow interior having a generally cylindrical inner surface, at leasttwo portions of the inner surface departing from an open-end thereof,differing from each other and from the other portion of the innersurface in shape, and the hollow interior having a cross-sectional areaat at least one of the two portions larger than that of the hollowinterior at the open end, and a filler body in the plunger body interiorand having portions received in the two portions of the inner surface toprevent axial, spiral and circumferential displacements of the fillerbody relative to the plunger body.

The invention will be better understood and other objects and additionaladvantages of the invention will become-apparent upon perusal of thefollowing description taken in connection with the drawings, in which:

FIG. 1 is a longitudinal section of a hydraulic fluid pressuretranslating device incorporating one embodiment of the presentinvention;

FIG. 2 is a central sectional view on-an enlarged scale of the improvedplunger construction used in connection with the device illustrated inFIG. 1;

FIG. 3 is a cross-sectional view thereof taken alongthe line 33 ofFIG.2; and

FIG. 4 is a central sectional view on an enlarged scale of anotherembodiment of this invention.

Similar numerals refer to similar parts throughout the several views.

While this invention is susceptible to embodiment in many differentforms, there are shown in the drawings and will herein be described indetail two embodiments of the invention, with the understanding that thepresent disclosure is to be considered as an exempliflcation of theprinciples of the invention and is not intended to limit the inventionto the particular embodiments illustrated. The scope of the inventionwill be pointed out in the appended claims.

Referring now to the drawings, and particularly to FIG. 1, an axialplunger type of hydraulic fluid pressure translating device is shown.The axial pump or motor includes a housing indicated generally at 10having an end plate 11 removably secured thereto. A drive shaft 12 isrotatably supported at opposed ends of housing 10 by suitable bearings15 and 16, which also secure drive shaft12 against axial movement. Theshaft 12 is drivingly connected, as by splines 13, to a cylinder block14 for rotation of cylinder block 14 and drive shaft 12 together.

The cylinder block 14 includes plungers, two of which are shown at 20,reciprocally mounted within bores or cylinders 23 in the cylinder block14. Although only two plungers are shown in FIG. 1, it is to beunderstood that the cylinder block 14 includes a circumferentiallyarranged plurality of axially disposed cylinders within the cylinderblock, each cylinder having an inner end of a plunger reciprocatingtherein.

The outer ends 21 of the plungers 20 are spherical ends, which are inengagement with slippers 34 so as to be rotatably and swingably held bythe latter. The slipper 34 is rotatably mounted on a swash plate 31which is swingable within the housing 10 about an axis 33 transverse toand intersecting the axis of the drive shaft 12.

When the drive shaft 12 is externally driven by a suitable means, thecylinder block 14 is rotated, and therefore, the plungers 20 are alsorevolved on the axis of the'drive shaft 12. Because the swash plate 31in inclined to the axis of the drive shaft 12, the plungers 20 arereciprocated relative to the cylinders 23 for pumping. The liquid mediumsucked into a cylinder from an inlet 17 through a port plate 19 isexhausted to an outlet 18 through the port plate 19 after a half turn ofthe drive shaft 12 under a pressure.

As is best seen in FIG. 2 and FIG. 3, the plunger 20 includes an axiallyelongated body 200 which is generally cylindrically shaped, and whichincludes a portion of reduced'diameter'201 adjacent the forward endthereof which merges into the spherical end 21. The plunger 20 ispreferably formed of a wear resistant material that is capable ofwithstanding high stresses, such as a heat treated steel or steel alloy.In order to reduce the weight of the plunger 20, an'axially elongatedgenerally cylindrical cavity 202 is formed generally centrally therein,and extends substantially the entire length of the body 202. An axiallyextending centrally disposed opening 203 is formed in the forward end ofthe plunger 20, the purpose of which will hereinafter become apparent.

In order to prevent adverse compressibility effects due to the presenceof liquid medium in the cavity 202, a filler body 204 is provided in thecavity 202. The filler body 204 is preferably an inert, light-weightmaterial of sufficient high bulk modulus as to avoid significantcompression by the liquid medium. Lightgweight metallic materials suchas aluminum or magnesium, and alloys thereof, are suitable for thispurpose. Thermo-setting artificial resins are also suitable for thispurpose. Such a material may be conventionally transfer molded orcompression molded into the cavity 202. Other materials may be poured orinjection molded, if desired. The cavity 202 in the plunger may beformed by drilling, or if desired, the plunger 20 may be forged with thecavity 202 being formed in the forging operation. A central axiallyextending hole 205 is formed in filler body 204, and is positioned inalignment with the hole 203 in the forward end of the plunger 20, toallow liquid medium to flow through the plunger from the cylinder 23 toprovide lubrication to the forward end of the plunger 20, and tohydrostatically balance the slipper 34.

Novel means are provided for retaining the filler body 204 againstaxial, spiral and circumferential displacements within the plungerchamber 202, including at least two portions of the generallycylindrical inner surface areas of the plunger chamber 202. Inaccordance with this embodiment, the two portions 206 and 207 are formedin a single generally circumferential groove in the inner surface. Thatis to say, the single circumferential groove is radially formed and hasvarying depth. A portion 207 of the groove is deeper than anotherportion 206 from the general inner surface of the plunger chamber 202.The groove may be an ellipse in the diametrical direction of the plungerchamber 202 in view of machining operation. The elliptic groove has thetwo deepest portions 207 and four intermediately deep portions 206. Byvirtue of e the above-mentioned manner for forming the filler body 204,

it completely fills the groove having the portions 206 and 207,

and therefore, the filler body 204 is restricted not only from axialdisplacement but also, at the same time, from any spiral and/orcircumferential displacement relative to the plunger body 200. In orderto prevent the axial displacement of the filler body 204 relative to theplunger body 200, it is also noted that, in accordance with thisinvention, the filler body 204 has a portion where the cross-sectionalarea is larger than that of the end 208 thereof.

Reference is now made to FIG. 4 illustrating another embodiment of aplunger 20 in accordance with this invention. The plunger 20' is madesimilarly to the plunger 20 of the first embodiment, but is formed witha different cavity 212. The plunger cavity 212 is also generallycylindrical, but has an intermediate part 213. A portion 215 situateddeeper in cavity 212 than the intermediate part 213 of the generallycylindrical inner surface of the plunger cavity 212 is formed with ascrew thread groove. Another portion 216 before the intermediate part213 towards the open-end of the plunger cavity 212 of the inner surfacethereof is formed with another screw thread groove. The two screw threadgrooves 215 and 216 are different in pitch, and particularly, in apreferred embodiment, one of the two pitches is positive forming aright-hand thread while the other is negative forming a left-handthread, so that these two screw thread grooves 215 and 216 are to beturned in opposite directions for axial displacement in the samedirection. For facilitating the machining, the plunger cavity 212 has asmaller diameter in the portion 215 than the portion 216. It ispreferred that the screw thread groove 216 is not axially extended up tothe open-end of the plunger cavity 212, so that a part 217 of theplunger cavity 212 remains without being formed with the groove 216. Afiller body 214 is formed similarly to the preceding embodiment, so thatthe two screw threads are formed in the generally cylindrical outersurface thereof and completely complement and fill the recessive innerscrew thread groove 215 and the outer screw thread groove 216 which isnearer to the open-end of the plunger body 210. By virtue of these screwthreads, of which the pitches are different from each other, the fillerbody 214 is restricted not only from axial displacement but also, at thesame time, from any spiral and/or circumferential displacement relativeto the plunger body 210.

Thus, it will be seen that with both embodiments of the invention theplunger has a plunger body formed with a bore extending axially alongthe interior of the plunger body from one end thereof and defined by theinner generally cylindrical surface of the plunger body. This bore isfilled by the filler body which has an outer surface directly engagingand completely complementary to the inner surface. One of these surfacesis formed with surface cavities and the other of the surfaces is formedwith surface projections complementary to and filling the cavities, andall of these surface cavities and projections are situated inwardly ofthe end of the plunger body up to which the filler body extends so thatthese complementary surface cavities and projections prevent axialdisplacement of the filler body out of the plunger body. In the case ofFIGS. 2 and 3, the complementary surface cavities and projections formthe substantially elliptical enlargement of the filler body which isillustrated in FIG. 3, and it will be noted that this enlargement isformed by a pair of projections of the filler body having the portions206 and 207 which are of a gradually diminishing radial depth withrespect to the generally cylindrical inner surface of the plunger body,with each projection extending circumferentially about the axis of theplunger body through approximately to provide the cross section of thefiller body which is illustrated in FIG. 3. As a result the pair ofcomplementary surface cavities and projections shown in FIG. 3 willprevent circumferential as well as axial movement of the filler bodywith respect to the plunger body.

In the case of FIG. 4, the complementary surface cavities andprojections are in the form of the illustrated screw threads 215 and 216with the screw thread 216 having a larger diameter than the screw thread215 and forming a thread of characteristics different from the thread215 so that in this case also the complementary surface cavities andprojections serve to prevent both circumferential and axial movement ofthe filler body with respect to the plunger body.

While particular embodiments of this invention have been illustrated anddescribed, modifications thereof will readily occur to those skilled inthe art. It should be understood therefore that the invention is notlimited to the particular constructions disclosed but that the appendedclaims are intended to cover all modifications which do not depart fromthe true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

l. A plunger for a pump or motor, comprising an elongated plunger bodyformed with a bore extending axially along the interior of said plungerbody from one open end thereof and defined by an inner surface of saidplunger body which is of a generally cylindrical configuration, a fillerbody situated within and filling said bore of said plunger body, saidfiller body having an outer surface which is complementary to andengages the entire area of the inner surface of said plunger body, saidsurfaces being formed respectively with complementary surface cavitiesand surface projections which respectively completely fill saidcavities, an axial space defined between said one open end of saidplunger body and said surface cavities and projections, said axial spacehaving a radial dimension less than the radial dimension of the nearestcomplementary surface cavity and projection, whereby all said surfacecavities and projections are situated inwardly of said one end of saidplunger body up to which said filler body extends, so that all of saidcomplementary surface cavities and projections are axially displacedaway from said one end of said plunger body for preventing axialmovement of said filler body out of said plunger body through said oneend of the latter, each of said complementary surface cavities andprojections extending at least through approximately 180 about the axisof said plunger body, and said plurality of complementary surfacecavities and projections having a configuration which prevents axial,spiral, and circumferential movement of said filler body with respect tosaid plunger body.

2. The combination of claim 1 and wherein there are only two surfacecavities and complementary surface projections respectively filling saidsurface cavities.

3. The combination of claim 2 and wherein said two complementary surfacecavities and surface projections respectively filling said cavities arecircumferentially displaced with respect to each other through 180 aboutthe axis of said plunger body but are in axial alignment with respect toeach other, with each of the surface cavities and the surfaceprojections filling the latter having a configuration which provide eachsurface projection with a radial dimension with respect to the plungerbody axis which gradually increases through approximately 90 anddecreases through the remaining 90, so that the pair of complementarysurface cavities and projections form in cross section an area ofsubstantially elliptical configuration.

4. The combination of claim 1 and wherein said complementary surfaceprojections and cavities are in the form of screw threads whichrespectively differ from each other so that turning at one of the screwthreads will result in binding at another of the screw threads.

5. The combination of claim 4 and wherein said screw threads which formthe complementary surface cavities and projections are axially displacedwith respect to each other along the axis of said plunger body.

6. The combination of claim 5 and wherein there are only two screwthreads forming a pair of surface cavities and complementary surfaceprojections filling the surface cavities.

7. The combination of claim 6 and wherein said two screw threads arelocated one nearer to said one end of said plunger body than the other,and that one of said screw threads which is nearer to said one end ofsaid plunger body having a diameter greater than the other of the screwthreads.

8. The combination of claim 6 and wherein said two screw threads arerespectively a left-hand thread and a right-hand thread.

1. A plunger for a pump or motor, comprising an elongated plunger bodyformed with a bore extending axially along the interior of said plungerbody from one open end thereof and defined by an inner surface of saidplunger body which is of a generally cylindrical configuration, a fillerbody situated within and filling said bore of said plunger body, saidfiller body having an outer surface which is complementary to andengages the entire area of the inner surface of said plunger body, saidsurfaces being formed respectively with complementary surface cavitiesand surface projections which respectively completely fill saidcavities, an axial space defined between said one open end of saidplunger body and said surface cavities and projections, said axial spacehaving a radial dimension less than the radial dimension of the nearestcomplementary surface cavity and projection, whereby all said surfacecavities and projections are situated inwardly of said one end of saidplunger body up to which said filler body extends, so that all of saidcomplementary surface cavities and projections are axially displacedaway from said one end of said plunger body for preventing axialmovement of said filler body out of said plunger body through said oneend of the latter, each of said complementary surface cavities andprojections extending at least through approximately 180* about the axisof said plunger body, and said plurality of complementary surfacecavities and projections having a configuration which prevents axial,spiral, and circumferential movement of said filler body with respect tosaid plunger body.
 2. The combination of claim 1 and wherein there areonly two surface cavities and complementary surface projectionsrespectively filling said surface cavities.
 3. The combination of claim2 and wherein said two complementary surface cavities and surfaceprojections respectively filling said cavities are circumferentiallydisplaced with respect to each other through 180* about the axis of saidplunger body but are in axial alignment with respect to each other, witheach of the surface cavities and the surface projections filling thelatter having a configuration which provide each surface projection witha radial dimension with respect to the plunger body axis which graduallyincreases through approximately 90* and decreases through the remaining90*, so that the pair of complementary surface cavities and projectionsform in cross section an area of substantially elliptical configuration.4. The combination of claim 1 and wherein said complementary surfaceprojections and cavities are in the form of screw threads whichrespectively differ from each other so that turning at one of the screwthreads will result in binding at another of the screw threads.
 5. Thecombination of claim 4 and wherein said screw threads which form thecomplementary surface cavities and projections are axially displacedwith respect to each other along the axis of said plunger body.
 6. Thecombination of claim 5 and wherein there are only two screw threadsforming a pair of surface cavities and complementary surface projectionsfilling the surfacE cavities.
 7. The combination of claim 6 and whereinsaid two screw threads are located one nearer to said one end of saidplunger body than the other, and that one of said screw threads which isnearer to said one end of said plunger body having a diameter greaterthan the other of the screw threads.
 8. The combination of claim 6 andwherein said two screw threads are respectively a left-hand thread and aright-hand thread.